Process for the filling of leather



'bution in the leather.

Patented Sept. 11, 1962 3,053,697 PROCESS FOR THE FILLING F LEATHER Bruno Zorn, Koln-Deutz, Wolfhard Luck, Koln-Stammhelm, and Gustav Mauthe, Opladen, Germany, assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany No Prawing. Filed May 12, 1958, Ser. No. 734,411

Claims priority, application Germany May 17, 1957 13 Claims. (Cl. 117-142) The present invention relates to and has as its objects an lmproved process for the filling of leather with certain dispersions of finely divided solid particles.

The embedding of finely divided solid fillers into leather in the presence of dispersing agents is known. It is the purpose of the dispersing agents to conserve the finely divided form of the fillers and to ensure their even distri- In general, the dispersing agents themselves do not improve the plumpness of the leather and they rather detrimentally affect the water absorption of the leather.

It has now been found that finely divided solid fillers may advantageously be embedded in the leather with dispersing agents which are Water-soluble products precipitable by acids and obtainable in known manner from dicyandiamide, formaldehyde and water-soluble dispersing salts of organic sulfonic acids, especially the sodium salt of dinaphthyl methane disulfonic acid; an acid, or a compound having an acid reaction in aqueous solution being added before, during or after the embedding of the fillers, and the leather having a pH value of less than 7, preferably of 3.5-5.5, at least at the end of the treatment.

The products to be used as dispersing agents are obtainable in known manner (for example according to the instruction of US. patent specification No. 2,737,504 or according to the instruction of copending applications Serial No. 5110, 861, filed May 24, 1955, and now US. Patent No. 2,884,403, Serial No. 688,121, and Serial No. 661,000). Briefly summarized, according to these copending applications dicyandiamide, urea, melamine and the like, and formaldehyde may be condensed at a pH value of more than 7 in the presence, if desired, of water-soluble monoor polyhydric alcohols and/ or water-soluble mono or poly-saccharides and/or water-soluble salts of sulfurous acid and/ or other compounds condensable with oxo-compounds, such as urea or melamine, and there may be added before, during or after the condensation a water-soluble, dispersing salt of an organic sulfonic acid, especially the sodium salt of dinaphthyl methane disulfonic acid, and the condensation is allowed to proceed as long as the condensation products containing the aforesaid salt are still Water-soluble.

In contrast to the dispersing agents used in known manner for the embedding of fillers in the leather, the aforesaid acid-precipitable products contribute to the improvement of the leather plumping and, since they are easily convertible into a water-soluble state, they impair the water-absorption of the after-treated leather only to a lesser degree. The dispersing agents applicable according to the invention have an afiinity for the leather fibre and not only act as carriers for the fillers but also improve the fixation of the fillers in the leather as they are insolubilized during or after the embedding process. During the conversion of the compounds applicable as dispersing agents according to the invention into an insoluble form, the fillers are obviously covered by these compounds thus fixing them to the fibre.

As fillers according to the definition of this patent application there may be used, for example, finely divided silicic acid, calcium silicate, magnesium silicate, aluminiurn silicate and the like, aluminum oxide, meal aluminates such as calcium aluminate, magnesium aluminate and the like, titanium dioxide, carbon black, iron oxide pigments, metal titanates, naturally occuring silicates, aluminates and the like, such as china clay, kaolin, diatomaceous earth, kieselguhr, talc, gypsum, barium sulfate, zinc sulfide or mixtures thereof and the like. Furthermore organic fillers may be used such as polyvinyl chloride or vinyl copolymerisate, butadiene styrene copolymerisates, finely divided cellulose, starch and derivatives thereof, especially ethers, insoluble urea formaldehyde condensates and the like.

The proportion of the products applicable as dispersing agents with respect to the fillers may vary within a wide range, and depends largely upon the filler or the dispersing agent to be used. Thus, 100 parts of the mixture of the inventive dispersing agent and filler may contain from about 1 part to parts of filler. Usually, however, the inventive mixture contains between 10 to 50% of filler. The particle size of the filler usually should be at least less than 0.05 mm., but preferably between about 0.1 to 50a. The amount of the inventive mixture of dispersing and filling agent used in practice is from about 1 to 30% (of dry substance), but especially 3 to 10% referred to the Wet tanned leather (e.g. shaved weight of chrome tanned leather or drained weight of leather of other tanning origin). Leather in the meaning of this application concerns all tanned hides either minerally tanned, especially chrome tanned, vegetable tanned or organic synthetic tanned leather or combined tannages thereof.

In contrast to the dispersing agents used according to known methods for the embedding of fillers, even large quantities of the products applicable as dispersing agents according to the invention may be employed not only without risk but in some instances even with advantage since these products themselves improve the plumpness of the leather to be treated. Excess quantities of the products to be used as dispersing agents according to the invention may readily be converted into an insoluble form by the addition of acids or compounds having an acid reaction in aqueous solution, to the treating bath or to the leather.

The addition of acids such as hydrochloric acid, sulfonic acid, boric acid, formic acid, acetic acid, propionic acid, lactic acid, organic sulfonic acids such as methane sulfonic acid, benzene sulfonic acid, dinaphthyl methane disulfonic acid and the like, or compounds having an acid reaction in an aqueous solution such as chromium, aluminium, zirconium or zirconyl salts of strong acids, is advantageously effected towards the end of the embedding process. In some cases the addition may be dispensed with, especially when the leather possesses at the end of the treatment a high acidity, i.e. a pH value of less than 7, preferably of 4.5-5.5

The following examples are given for the purpose of illustra-ting the invention.

Example 1 parts of a cow hide chrome tanned in conventional manner and shaved to a thickness of 1.8 millimeters are neutralized at 35 C. with 1 part of calcium formate and 0.8 parts of sodium bicarbonate in 300 parts of water so that the moist leather out has a pH value of 5.6. After briefly rinsing, the leather is milled with a mixture of 3 parts (solids) of a resin obtainable according to Example 1 of US. patent specification No. 2,737,504, and 3 parts of calcium silicate having a particle size of 10 microns and parts of water at 60 C., for 45 minutes. After this period of time the liquor is to have a pH valve of 5.2. The dispersing agent and filler is then well absorbed by the leather. It is dyed and liquored in conventional manner and dried according to the pasting process. The leathers thus obtained have, compared with the pure a chrome tanned leather, an improved plumpness, good grain resistance and pleasant handle in addition to level dyeing, especially at the marginal parts of the hide.

Example 2 The process is carried out as indicated in Example 1 using a resin obtainable in analogous manner, but adding to the reaction mixture another 120 parts of isopropyl alcohol before the condensation starts. The condensation time, as against that of Example 1, is prolonged to -6 hours until the water-insoluble state is attained.

The leather thus obtained shows similarly improved properties to that obtained according to Example 1.

Example 3 The process is carried out as indicated in Example 1 but instead of calcium silicate there is used a commercial finely dispersed silicic acid, having a particle size of 0.02- 0.1 micron. There is likewise obtained a leather with increased plumpness.

Example 4 100 parts of shaved chrome-tanned calf skins are thoroughly rinsed with warm water at 50 C. and then milled at 60 C. for 1 hour with a mixture from 5.2 parts of the resin described below and 0.4 part of a commercial titanium dioxide pigment in 120 parts of water. After this time, the filling and dispersing agent is well absorbed by the leather. The pH value of the liquor should be 5.0-5.4. The leather is briefly rinsed and stuifed with a fat-liquoring agent fast to light.

Compared with all-chrome tanned calf leather, the leather thus obtained has a stronger grain and a lighter color. The dressing ability of the leather is very good.

Preparation of the resin: 84 parts of dicyandiamide, 60 parts of urea and 162 parts of a 37% formaldehyde solution (containing about of methanol) are refluxed with stirring at 96-98 C. in the presence of 72 parts of sodium dinaphthyl methane disulfonate and 76 parts of a 50% delimed and neutral sulfite waste liquor until a sample of the product dissolves clearly in water and yields with 1 N acetic acid a strong precipitate.

Example 5 The process is carried out as indicated in Example 4 but instead of titanium dioxide there are used 0.4 part of a finely divided kaolin and 7 parts of a resin obtained in the following manner: 84 parts of dicyandiamide, 28.5 parts of sodium meta-bi-sulfite, 325 parts of 37% formaldehyde and 135 parts of an approximately 50% idelimed and neutral sulfite waste liquor are heated under reflux for 4 hours.

The leather obtained according to this process shows, when compared with pure chrome leather, improved properties similar to those produced according to Example 4.

Example 6 100 parts of shaved bark-tanned sheepskin are briefly rinsed and then milled at 35 C. for 10 minutes with 80 parts of water and 1% of a medium sulfonated sperm oil. A mixture of 4 parts (calculated on dry substance) of a condensation product is then added, obtained as indicated in Example 1, 4 parts of a finely divided polyvinyl chloride and 2 parts of a neutral condensation prod uct from dihydroxy diphenyl sulfone, formaldehyde and naphthalene-sulfonic acid, obtainable for example according to the instruction given in Example 1 of German patent specification No. 611,671, and the leather is milled for 30 minutes. 0.8% of anhydrous aluminium sulfate or 1% of boric acid are then added and the leather is milled for a further 20 minutes. The pH value should then be between 4 and 5. Well plumped and grain-resistant leathers are obtained which can be further processed in the usual way.

We claim:

1. Process for the filling of leather which comprises milling leather with a finely divided filler in the presence of a water-soluble dispersing agent, precipitable by acid, obtainable by condensation of carbamide with formaldehyde in a nonacid medium and containing a water-soluble salt of an organic sulfonic acid, and in the presence of sufiicient acid to precipitate the dispersing agent.

2. Process for the filling of leather which comprises milling leather with a finely divided filler in the presence of a water-soluble dispersing agent, precipitable by acid, obtainable by condensation of dicyandiamide with formaldehyde in a nonacid medium and containing a watersoluble salt of an organic sulfonic acid, and in the presence of sutficient acid to precipitate the dispersing agent.

3. Process for the filling of leather which comprises milling leather with a finely divided filler in the presence of a water-soluble dispersing agent, precipitable by acid, obtainable by condensation of dicyandiamide and urea with formaldehyde in a nonacid medium and containing a water-soluble salt of an organic sulfonic acid, and in the presence of sufficient acid to precipitate the dispersing agent.

4. Process for the filling of leather which comprises milling leather with a finely divided filler in the presence of water-soluble dispersing agent, precipitable by acid, obtainable by condensation of dicyandiamide and melamine With formaldehyde in a nonacid medium and con taining a water-soluble salt of an organic sulfonic acid, and in the presence of sutficient acid to precipitate the dispersing agent.

5. Process for the filling of leather which comprises milling leather with a finely divided filler in the presence of a Water-soluble dispersing agent, precipitable by acid, obtainable by condensation of dicyandiamide melamine and urea with formaldehyde in a nonacid medium and containing a water-soluble salt of an organic sulfonic acid, and in the presence of sufiicient acid to precipitate the dispersing agent.

6. Process for the filling of leather which comprises milling leather with a finely divided filler in the presence of a water-soluble dispersing agent, precipitable by acid, obtainable by condensation of dicyandiamide with formaldehyde in a nonacid medium and containing a Watersoluble salt of an organic sulfonic acid, and finishing the milling process by adjusting the medium to a pH value from 3.5 to 5.5.

7. A process for the filling of leather which comprises milling leather with an alkaline dispersion comprising a finely-divided filler and a water-soluble dispersing agent precipitable by acid obtainable by condensation of a carbamide with formaldehyde in a nonacid medium and containing a water-soluble salt of an organic sulfonic acid and finishing the milling process by adjusting the dispersion to a pH of less than 7.

8. A process for the filling of leather which comprises milling leather having a pH of less than 7 with a dispersion of a finely-divided filler and a water-soluble dispersing agent precipitable by acid obtainable by condensation of a carbamide with formaldehyde in a nonacid medium and containing a water-soluble salt of an organic sulfonic acid, said leather containing sufi'rcient acid to precipitate the dispersing agent in situ.

9. A process for the filling of leather which comprises milling leather with a finely-divided filler in the presence of a water-soluble dispersing agent precipitable by acid obtainable by condensation of dicyandiamide and urea with formaldehyde in a nonacid medium and containing a water-soluble salt of an organic sulfonic acid and in the presence of sufficient acid to precipitate the dispersing agent.

10. A process for the filling of leather in accordance with claim 9 in which the filler is kaolin and the dispersing agent includes a resin obtainable by condensation of sodium metabisulfite, formaldehyde and delirned, neutral sulfite Waste liquor.

11. A process for the filling of leather in accordance with claim 9 in which the dicyandiarnide-urea-formaldehyde resin is applied With a finely-divided polyvinyl chloride and a dispersing agent obtainable by the condensation of dihydroxy diphenyl sulfone, formaldehyde and naphthalene sulfonic acid.

12. A filled leather product impregnated with a finelydivided filler bonded to the resin by a Water-insoluble condensation product of a carbamide and formaldehyde, initially condensed in a nonacid medium and containing a Water-soluble salt of an organic sulfonic acid, and precipitatcd in situ in the leather.

13. A filled leather product impregnated with a finelydivided filler bonded to the resin by a water-insoluble condensation product of dicyandiamide and form-aldehyde, initially condensed in a nonacid medium and containing a Water-soluble salt of an organic sulfonic acid, and precipitated in situ in the leather.

References Cited in the file of this patent UNITED STATES PATENTS 2,353,556 Grim et a1. July 11, 1944 2,367,446 Strobino Jan. 16, 1945 2,474,909 Olpin et al July 5, 1949 2,544,691 Kngler et al Mar. 13, 1951 2,567,238 Sellet et al Sept. 11, 1951 2,686,764 Geister et al; Aug. 17, 1954 2,737,464 Dawson et a1 Mar. 6, 1956 2,737,504 Dawson etal Mar. 6, 1956 2,828,222 Kine et a1 Mar. 25, 1958 

1. PROCESS FOR THE FILLING OF LEATHER WHICH COMPRISES MILLING LEATHER WITH A FINELY DIVIDED FILLER IN THE PRESENCE OF A WATER-SOLUBLE DISPERSING AGENT, PRECIPITAABLE BY ACID, OBTAINABLE BY CONDENSATION OF CARBAMIDE WITH FORMALDEHYDE IN A NONACID MEDIUM AND CONTAINING A WATER-SOLUBLE SALT OF AN ORGANIC SULFONIC ACID, AND IN THE PRESENCE OF SUFFICIENT ACID TO PRECIPITATE THE DISPERSING AGENT. 